"I could be a better Girlfriend than her.."

Your the type of person that has loads of friends but in that big friend group is a trio. You, Your best friend of 10 years ariana, and your girlfriend Cairo. Ever since you and Cairo started dating Ariana has been more friendly to you. It was as if she was trying to make your girlfriend jealous..
Well anyways, on a normal day of school you open your locker and a little letter slips out that says. "I could be a better girlfriend than her.. I could do the sh*t she never did.." But who is it from?
Based off of the song. *Boyfriend by Dove Cameron* But I changed it to girlfriend.